Archive for the ‘GOES Products’ Category

I didn’t have a chance to make this post last week when the imagery were more time-relevant. Nevertheless, I wanted to point out another example of the usefulness of MODIS and VIIRS imagery over current GOES imagery and show the usefulness of exciting products and imagery to come! First, let’s take a look at the color-enhanced GOES-IR image below from the morning (0715 UTC) of June 20th.

I’ve placed the yellow circles in the image for a reason, which you’ll see below. Further down, I’m going to show areas of fog displayed in the MODIS and VIIRS imagery, and granted, this is not the standard GOES channel difference (11-3.9 µm) typically used for making fog assessments. However, this post is meant to show current (MODIS / VIIRS) and future capabilities (GOES-R / JPSS) that will make fog detection and cloud differentiation much more easy for the operational forecaster. So, in the image above, fog is nearly unidentifiable as it was in the 11-3.9 µm channel difference image that morning (not shown). Mainly high cirrus clouds can be observed scattered across the region. Now, let’s take a look at the MODIS “fog” product, or channel difference (11-3.9 um) product valid at about the same time (Image 2).

Notice that in the same areas we can now begin to see low clouds (indicated by yellow colors) scattered around the valleys of the southern Appalachian region. While the GOES-East imager is capable of detecting larger scale fog often in the valleys in the eastern circle, fog in the valleys in the western circle present challenges for the current GOES-East instrument, and is often not shown very well (even in the standard 11-3.9 µm channel difference). Next, let’s take a look at a VIIRS Nighttime Microphysics RGB valid at about the same time.

Image 3. VIIRS Nighttime Microphysics RGB valid 0723 UTC 20 June 2014

In the RGB imagery it is much easier to detect the extent of the fog, making the operational forecast process much more effective. Notice also that it is possible to see the fog through the higher clouds around the TN/GA/NC border region. Not only does the resolution of the VIIRS and MODIS instruments allow for superior fog detection, but the RGBs in particular offer tremendous operational advantages. As a user of RGBs for about 2 years now, I am convinced that this type of imagery has a relevant and needed place in future operational forecasting. Of course, it will take time for forecasters to become accustomed and adjust to the new imagery, but it will happen.

Shortly after arriving for my evening shift today, I was called by a representative from an organization hosting an outdoor event in downtown Huntsville. She was inquiring about the chances for shower or thunderstorm development into the early evening hours during the outdoor event (movie in the park night). As I have grown quite accustomed to loading the GOES-R CI and total lightning products to be used for situational awareness, especially during the convective season, I referred to those to help with my assessment…in addition to radar data of course. The image below shows GOES Visible channel imagery overlaid with GOES-R CI, total lightning data, and NLDN (the latter of which may be hard to see). The location of Huntsville is labeled, and cloud motion is analyzed in the image. Notice that the GOES-R CI product indicates generally low probabilities of convection in the area of clouds to the northwest (and upstream) of Huntsville. The blue colors indicated CI probabilities of around 10-40%.

Notice that only a few showers were located to the NW of Huntsville, but the GOES-R CI suggested further development was not likely and the total lightning (available from the North Alabama LMA) suggested these were only showers and thus not electrically active (I had looked over the previous ~20-30 mins). Notice that lightning activity was relegated mainly to the South and East of the area. This was a situation in which the GOES-R CI and total lightning data both served to provide a more complete assessment of the situation, allowing for a better forecast for one of our customers.

By the way…my forecast to her? Well, based on the evidence from the observational imagery/data…I said very small chances for any shower activity, so let the show go on! No showers ended up impacting the downtown area.

This was one of those storms that people will talk about for years, especially those that were directly affected by it. It all started with three separate shortwaves that all phased together once off the Mid-Atlantic coast, far enough offshore to limit any direct effects save for some unusual late season snow and gusty winds the next day. The highest impact area included Cape Cod, Nantucket, Nova Scotia, and New Foundland. I’m sure any ships that were in the vicinity were not happy with this situation!

GOES-Sounder RGB Air Mass animation valid 03/24/14-03/26/14.

The evolution of the nor’easter can be seen in the GOES Sounder RGB Air Mass animation above. A southern stream system originating in the Gulf of Mexico moved east of Florida while two other shortwaves dropped southeast out of Canada. All of the pieces combined near the North Carolina coastline, but the explosive deepening took place as the combined system moved northeast away from the Mid-Atlantic. There appears to be a few stratospheric intrusions, but the most impressive intrusion occurs with the final shortwave as noted by the dark oranges and reds that appear at the end of the day on 03/25. When models are forecasting a phasing situation, this product can be quite useful in identifying the features and observing the stratospheric drying seemingly “bleed” from one shortwave to the other.

The two MODIS RGB Air Mass products above show the nor’easter near peak intensity. Notice how distinct the gradient between oranges and greens is in this image, almost as though you can see the upper portion of the frontogenesis, well behind the actual front. The intensity of the stratospheric intrusion is quite evident by the dark pinks near the center of the cyclone. The second image shows the wind field overlaid from ASCATB. Notice the large area of hurricane force winds (red wind barbs) near the bent-back front, in the comma-head of the cyclone. This area of wind affected parts of Southeast Massachusetts, including Nantucket where winds gusted from 60-85 mph. Nantucket recorded a wind gust of 82 mph and about 10″ of snow. Meanwhile, Nova Scotia bore the brunt of this beast with wind gusts of 129 mph at the Bay of Fundy and 115 mph in Wreckhouse. Waves were equally impressive with altimeter readings between 40-50 ft and a buoy report of 52.5 ft.

Another interesting aspect of this storm was the two distinct areas of thunderstorms that erupted. I overlaid the OPC and TAFB offshore zones for reference. Notice well east of the Bahamas there are possible supercell thunderstorms associated with the southern shortwave energy. Meanwhile, as the strong northern stream shortwaves exit the NC coastline, two areas of thunderstorms developed with the easternmost storm exhibiting supercell characteristics. Although the lightning was not as intense with this northern area, I would speculate that the storms were associated with very strong wind gusts due to the dry air associated with the stratospheric intrusion.

VIIRS Visible image valid at 1719 UTC on 03/26/14.

VIIRS Visible image with the 18 UTC OPC surface analysis overlaid.

I’ll finish this entry with two VIIRS Visible images above showing the majestic beauty of this nor’easter. The 18 UTC OPC surface analysis depicts the storm at a maximum intensity of 955 mb, after a 45 mb drop in 24 hours! This qualifies as one of the most explosive cyclones on record. Another tidbit. . .this was the strongest storm in this part of the Atlantic since Hurricane Sandy (2012).

Late yesterday evening (Dec 17th) fog began forming along coastal areas of Lousiana and Texas. By 10 pm CST, visibilities at some locations along the coast had already dropped to less than 1 SM. The fog continued to intensify, with visibilities falling to around 1/4 SM or less at many locations during the early morning hours this morning (Dec 18th). By 2 am CST (0800 UTC), the visibility had fallen to near 0 SM in portions of SW Louisiana as noted by the observation at Jennings (3R7, near Fenton in the image, image 1).

In this standard GOES spectral difference imagery however, the fog is very diffcult to visually discern, likely due to it’s very shallow depth. There is some indication of the fog, with slightly brighter pixels in areas of southern LA and SE Texas. However, notice the better (albeit slightly) detection of the fog in the Nighttime Microphysics RGB products from the VIIRS and MODIS instruments below (images 2 and 3, respectively). The fog in these images appears as a pinkish-gray color.

I think the fog is a little easier to see in the MODIS image, which may be due to higher resolution and small differences in channel wavelengths between the VIIRS and MODIS instruments. Nevertheless, the fog in all of the imagery is rather subtle and will require development of pattern recognition by forecasters. Sampling the color contributions, I found that the primary changes between areas of fog and areas without occurred in the green color (assigned the ~10.8-3.9/3.7 channel difference), which would be expected. For example, when taking a color sample from the pinkish-gray band of fog in SW Louisiana (near Jennings) from the MODIS image, I came up with: Red-180, Green-137, Blue-165. Meanwhile, sampling of a pixel in central Louisiana without fog: Red-167, Green-99, Blue-150.

So, how did the fog appear in the Day-Night Band RGBs? Not very well at all, as you can see in the next couple of images…

I wasn’t able to detect any fog at all in the Day-Night Band RGB imagery. However, there is still potentially important information to glean from all of this. If the fog is evident (even slightly) in the NT Microphysics RGB imagery mainly due to the 10.8-3.7/3.9 channel difference, but is essentially translucent in the visible spectrum (Day-Night Band), then it is likely very shallow. This could be helpful for determining the duration of the fog during a change of conditions, such as the development of mixing after sunrise (i.e. shallow fog dissipation will be quicker than thick fog dissipation).

Notice in the GOES visible loop below (images at 0445 UTC and 0601 UTC) that the fog dissipated very quickly after sunrise (click the expanded image to obtain the loop).

The Corpus Christi, Houston and Slidell offices all issued Dense Fog Advisories or Special Weather Statements concerning the fog in their respective County Warning/Forecast Areas during the early morning hours.

The RGB Imagery for Aviation and Cloud Analysis got underway on December 1st with SPoRT’s collaborative coastal NWS offices in Southern Region. These offices include Corpus Christi, Houston, Slidell, Mobile, Melbourne, and Miami. A separate evaluation with AK offices and CA/OR coastal offices has also begun recently. The SR coastal office evaluation will run through the end of January, where offices will be evaluating the VIIRS and MODIS Nighttime Microsphysics RGB imagery, VIIRS Day-Night Band Reflectance and Radiance RGBs, in addition to the hybrid GOES/MODIS/VIIRS 11-3.9 um looped product. SPoRT personnel have conducted training for the offices and will be helping during the evaluation with questions and/or technical issues. Although RGBs have been used in the European forecast community for years, they are quite new to most U.S. forecasters. However, and importantly, the imagery available from the Aqua/Terra satellites (MODIS imager) and the Suomi NPP satellite (VIIRS imager) are a part of GOES-R and JPSS Proving Ground activities and will serve as educational tools for forecasters before the GOES-R and JPSS eras. As a part of the evaluation, forecasters will answer a short survey about the operational impact of these imagery on aviation forecasts in particular, but may of course include impacts for other operational products (i.e. advisories, fire weather, public, hydrologic, etc).

While many potential positive impacts to various forecast products have been related on this blog, I’ll be watching and posting those which forecasters at these offices (and myself) observe during the evaluation period (time permitting of course). Take the following case from yesterday, December 9th, for example…

In the image above, notice the swath of light purple colors that extend across a good portion of the TX Gulf Coast. Further north, in north central and northeastern TX extending to include portions of Oklahoma, Missouri and Arkansas, an area of low clouds with colors closer to dull reds to greenish-white are apparent. In Image 1, a small area near Corpus Christi, TX has been sampled, with the contributions from Red (183), Green (132) and Blue (209) included in the image (This was sampled in Microsoft Paint). At about the same time, observations across this region of coastal TX were nearly uniform. Ceilings were around 300-400 ft from Houston, to Port Lavaca and Corpus Christi, with visibilities ranging from 1.5 to 2.5 SM.

Thus, the colors represented by the shades of light purple represented an extensive low stratus/fog deck encompassing the area. Notice that a swath of this color/cloud type also extended into northern Louisiana and Mississippi. Low visibilities ranging from 2.5 to 3 SM and low ceilings around 400 ft were observed in both areas.

Herein lies the power of the RGB imagery. Since the combination of colors are related to several physical characteristics (i.e. red – optical depth, green – particle phase and size, blue – temperature), then it is easier to make assessments about cloud homogeneity or inhomogeneity. While other satellite observations generally just relate one physical characteristic (usually temperature), or in the case of the standard 11-3.9 channel (particle phase/size), they don’t have the ability to tie together several physical characteristics together in one image like the RGBs can. It is thus much easier, with RGB imagery, to assess locations where cloud characteristics are the same and make inferences about the similarity of ceilings and visibility in areas without direct observations.

This next image shows a sample of the color taken from the Texarkana site in NE Texas at the same time, underneath the area of low stratus containing more dull red colors.

As the difference in colors suggests, the cloud characteristics are different here than in SE coastal TX. Referring to image 2, the ceiling and visibility at Texarkana were 1100 ft and 6 SM, respectively. Ceilings were still relatively low, but were higher than in coastal TX, as was the visibility. Essentially, this was a slightly higher stratus deck. The red color contibutions were very similar in each location, suggesting clouds of similar depth. However, differences in green and blue are clearly discernible. The cloud deck near the coast certainly contained more blue, indicating warmer temperatures, which makes physical sense. The clouds in NE TX contained more green however, which would suggest smaller water particle size. But, emssions in the 3.9 channel from the surface beneath the low/thin cloud deck near the coast may also be contributing to less green color there. Taking a look at proximity soundings in this area of clouds from Forth Worth (FWD) and Little Rock (LZK), cloud tops decreased during the 00-12 UTC period, but contained super-cooled water droplets by the 12 UTC sounding.

As an aside, forecasters have expressed the desire (including myself) to have the specific values from the red, green, blue color contributions available in AWIPS when sampling the imagery. This is a valuable part of the feedback and evaluation process. Unfortunately, this is not possible in AWIPS I, but will be in AWIPS II.

With the RGB Imagery for Aviation and Cloudy Analysis evaluation underway, we’re already getting some good feedback from our end-users. From WFO Morristown – “I looked at the Nighttime Microphysics product in hindsight to see how fog around TRI was depicted this morning. The (RGB) product did an outstanding job of clearly showing areas of fog vs. clouds, even though there were some thin midlevel clouds over the fog areas.” Below is a loop of the available MODIS (Aqua and Terra) and Suomi NPP VIIRS images from the southern Appalachain region early from late last evening through early this morning (click the image to see the loop).

The image shows the early production of fog (ligher, aqua colors) in the Cumberland and Allegheny Plateau region of eastern Kentucky and SW Virginia by the time of the first MODIS pass at 0359 UTC. Notice how the fog spreads to include other valley locations in East Tennessee by the time of the last images at 0736 UTC and 0810 UTC.

…and is even less noticable in the 4km GOES-East image alone a little later at 0832 UTC (image 3).

Image 3. GOES-East 11-3.9 µm image valid 0832 UTC, Sep 20 2013

Fog in the narrow valleys in the region shows up quite well in the VIIRS Day/Night Band Radiance RGB, developed by SPoRT (image 4). The forecaster noted that, “the DNB Radiance RGB showed fog clearly as well, but maybe not quite as well as the Nighttime Microphysics product.” I would agree, however I was encouraged by the detail and the relative ease with which fog was discernible in the image.

The typical issues with the timeliness of the polar-orbiting imagery, for opertional considerations, appears to be the largest concern for forecasters at this point in the survey process. Of course, this won’t be an issue in the GOES-R era, and acquanting forecaters with these types of imagery before the next generation of GOES satellites is launched is an important step in the learning process.

Showers and thunderstorms developed over the northern half of PR Sat Sep 14 and produced localized areas of 2 to 4 inches of rain that resulted in urban flooding and a new daily rainfall record at the San Juan (SJU) LMM Int’l Airport. A total of 2.88 inches fell at the SJU airport on Sat Sep 14 with 2.52 inches falling in less than 2 hours between 1145 AM and 130 PM. These showers and thunderstorms developed as a result of upper level diffluence ahead of an upper level low over the central Caribbean Sea aided by surface convergence due to sea breeze interaction and abundant moisture. Figure 1 below shows a four panel display of various water vapor channels from the GOES-Sounder and GOES imager overlaid with ECMWF model height fields and 15/00Z RAOB data. Figure 2 below shows the 12Z Sat Sep 14 Skew-T for SJU. Note the 20-35-kt south southwest flow at 300 and 200 mb on both the four panel display and the 12Z Skew-T respectively.

Animation of GOES-IR imagery (Fig. 3 below) with increased temporal resolution due to Rapid Scan Operations (RSO) in effect shows the development of showers and thunderstorms first over the San Juan area around 1445 UTC and then over north central and northwest PR through 2015 UTC. The imagery shows cold cloud tops ranging from -50C to -70C that were displaced to the north due to 20-35 kt south southwest flow aloft seen on the 12Z SJU RAOB data.

As part of GOES-R Proving Ground activities, WFO SJU continues to evaluate the NESDIS QPE product which uses mainly GOES-IR channel to estimate rainfall rates. Satellite based rainfall estimates for the 24-hr period ending 12 UTC Sun Sep 15 (Fig 4 below) showed up to an inch of rain fell just offshore of San Juan due to the coldest cloud tops being displaced to the north due to 20-35 kt south southwest flow seen on the 12Z upper air data.

Gauge data (Fig. 5 below) and Dual-Pol radar estimates (Fig. 6 below) indicate that in general between 1 to a little over 3 inches fell over parts of northern PR. This clearly indicates the need to continue to improve the GOES-R QPE algorithm to estimate rainfall and also to account for shear and cloud storm motions.